1. Field
The invention relates to a nickel-based brazing foil and a process for brazing two or more parts.
2. Description of Related Art
Soldering is a process for joining metal or ceramic parts using a melted filler material referred to as solder. The melting temperature of the solder is lower than that of the parent metals to be joined, which are wetted but not melted by the solder. A characteristic property of solders is their low melting range, i.e. the range between the solidus temperature and the liquidus temperature, and the resulting processing temperatures which typically lie 10° C. to 50° C. above the liquidus temperature.
A distinction is made between soft soldering and hard soldering, or brazing, depending on the processing temperature of the solder. Soft solders are processed at temperatures below 450° C., whilst hard solders, or brazes, are processed at temperatures above 450° C. Brazes are used in applications in which high mechanical stability of the soldered joint and/or high mechanical stability at high operating temperatures is desired.
Parts made of stainless steel, and of Ni- and Co-alloys are frequently joined using Ni-based brazes. These Ni-based brazes may also have a certain chromium content which results in improved corrosion resistance. In addition they may contain the metalloid elements silicon, boron and phosphorus which result in a reduction in the melting temperature and consequently the processing temperature of the braze. These elements are also referred to as glass-forming elements.
Ni—Cr-braze alloys are typically available in the form of solder powders produced using atomizing processes, or in the form of solder pastes in which the atomized powders are mixed with organic binding agents and solvents.
When brazing using solder pastes, the binding agents and solvents are decomposed. This can lead to inadequate flow and wetting behaviour and consequently to a poor joint. These problems can be avoided by using a braze in the form of a ductile foil, whereby a solder seam an be produced more reliably. Certain examples of Ni-based brazing foils which can be produced in the form of ductile foils are known from U.S. Pat. No. 4,316,572, for example. These ductile brazing foils can be produced by means of rapid solidification processes and are at least partially amorphous.